The invention relates to a free piston assembly comprising at least one piston accommodating device, at least one piston device which moves linearly in the corresponding piston accommodating device and has a first piston surface and a second piston surface that faces away from the first piston surface, and an expansion space which is formed in the piston accommodating device and is delimited by the first piston surface, wherein the piston device is arranged to be driven by the action of a medium which expands in the expansion space.
Furthermore, the invention relates to a method for controlling a free piston assembly which comprises a piston accommodating device, a piston device that moves linearly in the piston accommodating device and a resilience space.
With the aid of a free piston assembly for example, chemical energy can be partially converted by device of a combustion process into mechanical energy, namely the kinetic energy of a piston device, and then in turn, this mechanical energy can be converted at least partially into electrical energy using a linear drive. By arranging for the movement of the piston to be in the form of the movement of a free piston, a purely linear motion of the piston can be realized without the need to provide a crankshaft.
Devices of this nature can, for example, be employed as part of a hybrid drive for motor vehicles especially in connection with the concept of serial hybrid arrangements. They can also be employed as compact current generating units for generating electricity or else be utilised in connection with stationary applications such as engine-based cogeneration systems for example.
Free piston assemblies are known from GB 854 255 and DE 22 17 194 C3 for example.
Combustion devices with electrical generators are also known from U.S. Pat. No. 6,199,519 B1, DE 31 03 432 A1, DDR patent specification No. 113,593 and DE 43 44 915 A1 or from the article “Advanced internal combustion engine research” by P. van Barrigan, Proceedings of the 2000 DOE of Hydrogene Program Review.
From DE 102 19 549 B4, there is known a free piston assembly incorporating an electrical linear drive which comprises at least one piston accommodating device and at least one piston device that is arranged in the piston accommodating device such as to be moveable in a linear manner, wherein the piston device comprises a rotor assembly and wherein a stator assembly is arranged on the piston accommodating device. The at least one piston device is arranged to be driven by the action of a medium which expands in an expansion chamber, wherein the piston stroke is adapted to be varied by the linear drive in such a manner that the dead centres in the movement of the piston device are definable.
Another free piston assembly incorporating an electrical linear drive is described in WO 01/45977 A2.
From EP 1 398 863 A1, there is known a free piston assembly wherein a first displacement chamber, in which a piston in the at least one piston device upon which the medium is acting, is moveable, and a second displacement chamber in which the rotor assembly associated therewith is moveable, are separate chambers.
From DE 197 81 913 T1, there is known a method for controlling the movement of a linear generator, wherein the linear generator is driven by an internal combustion engine having two mutually opposed pistons aligned along a common axis. The current consumption is controlled in such a way that, during the back-and-forth cyclic movement of the generator, a resistive force is produced which is effective, substantially proportionately, on the generator at least in the central stroke range of the speed of movement of the generator. Pressure sensors are provided in the combustion chambers, a control unit triggering a device for igniting the mixture supplied to the combustion chambers when a predetermined pressure is reached.
A free piston assembly with an electrical linear drive is known from DE 10 2004 062 440 B4. The free piston assembly comprises a resilience chamber in which a gas is accommodated. At least one pressure sensor, by device of which the position and/or the speed of the piston device can be determined from a measurement of the pressure of the gas in the resilience chamber, is provided in the resilience chamber. Hence, with the aid of the measured pressure, a control and/or regulating process for the free piston assembly can be undertaken, for example, with respect to the injection of fuel into the expansion chamber, the ignition time point for the fuel in an expansion chamber and/or in regard to valves arranged on the expansion chamber.
From U.S. Pat. No. 5,002,020, there is known a hybrid engine which comprises a reciprocating piston and an electromagnetic transducer for control/regulation and power output purposes.
A free piston engine having a double action arrangement is known from the not prior published WO 2008/037980 A2. One piston is subjected to a conventional internal combustion cycle on one side and a steam expansion cycle on the other side.